Antitumor activity of an anti‐CD98 antibody

CD98 is expressed on several tissue types and specifically upregulated on fast‐cycling cells undergoing clonal expansion. Various solid (e.g., nonsmall cell lung carcinoma) as well as hematological malignancies (e.g., acute myeloid leukemia) overexpress CD98. We have identified a CD98‐specific mouse monoclonal antibody that exhibits potent preclinical antitumor activity against established lymphoma tumor xenografts. Additionally, the humanized antibody designated IGN523 demonstrated robust tumor growth inhibition in leukemic cell‐line derived xenograft models and was as efficacious as standard of care carboplatin in patient‐derived nonsmall lung cancer xenografts. In vitro studies revealed that IGN523 elicited strong ADCC activity, induced lysosomal membrane permeabilization and inhibited essential amino acid transport function, ultimately resulting in caspase‐3 and ‐7‐mediated apoptosis of tumor cells. IGN523 is currently being evaluated in a Phase I clinical trial for acute myeloid leukemia (NCT02040506). Furthermore, preclinical data support the therapeutic potential of IGN523 in solid tumors.     

Docetaxel suppresses invasiveness of head and neck cancer cells in vitro

The combination of docetaxel, cisplatin, and fluorouracil significantly enhances the survival of head and neck cancer patients compared to cisplatin and fluorouracil. We hypothesized that docetaxel may affect invasiveness of the head and neck cancer cells in addition to its tumor‐killing effect. Two different head and neck cancer cell lines (HEp‐2 and Ca9‐22) were treated with docetaxel at IC₁₀ and IC₅₀ concentrations. Cell migration and invasive growth was evaluated by wound healing assay and three‐dimensional (3D) culture of multicellular tumor spheroids, respectively. Expression levels of possible downstream effectors for cell migration/invasiveness were measured by immunoblotting in conditions with or without docetaxel. Docetaxel, but not cisplatin, suppressed filopodia formation compared with no treatment (control) condition. Consistent with this, docetaxel suppressed two‐dimensional (2D) cell migration and 3D cell invasion compared with control or cisplatin. Only docetaxel treated cells exhibited thick tubulin bundle and had lower activity of Cdc42, a member of the Rho family of small GTPases. In conclusion, Docetaxel treatment suppressed migration and invasiveness of head and neck cancer cells in vitro, which is likely to be mediated by regulating Cdc42 activity. (Cancer Sci 2010; 00: 000–000)     

Shikonin exerts antitumor activity via proteasome inhibition and cell death induction in vitro and in vivo

Dysregulation of the ubiquitin‐proteasome pathway plays an essential role in tumor growth and development. Shikonin, a natural naphthoquinone isolated from the traditional Chinese medicine Zi Cao (gromwell), has been reported to possess tumor cell‐killing activity, and results from a clinical study using a shikonin‐containing mixture demonstrated its safety and efficacy for the treatment of late‐stage lung cancer. In this study, we reported that shikonin is an inhibitor of tumor proteasome activity in vitro and in vivo. Our computational modeling predicts that the carbonyl carbons C₁ and C₄ of shikonin potentially interact with the catalytic site of β5 chymotryptic subunit of the proteasome. Indeed, shikonin potently inhibits the chymotrypsin‐like activity of purified 20S proteasome (IC₅₀ 12.5 μmol/L) and tumor cellular 26S proteasome (IC₅₀ between 2–16 μmol/L). Inhibition of the proteasome by shikonin in murine hepatoma H22, leukemia P388 and human prostate cancer PC‐3 cultures resulted in accumulation of ubiquitinated proteins and several proteasome target proapoptotic proteins (IκB‐α, Bax and p27), followed by induction of cell death. Shikonin treatment resulted in tumor growth inhibition in both H22 allografts and PC‐3 xenografts, associated with suppression of the proteasomal activity and induction of cell death in vivo. Finally, shikonin treatment significantly prolonged the survival period of mice bearing P388 leukemia. Our results indicate that the tumor proteasome is one of the cellular targets of shikonin and inhibition of the proteasome activity by shikonin contributes to its antitumor property. © 2008 Wiley‐Liss, Inc.     

A novel synthetic DNA minor groove binder, MS-247: antitumor activity and cytotoxic mechanism

Purpose: MS-247 is a novel synthetic compound possessing a DNA-binding moiety and a DNA-alkylating residue, chlorambucil. In this study, we evaluated the antitumor activity of MS-247 against murine tumor cell lines and its effects on DNA molecules in both cell-free and cellular systems. Methods: The in vitro cytotoxic activity of MS-247 was evaluated against four murine tumor cell lines, P388, L1210, Colon26 and B16, and its in vivo antitumor activity was also tested in comparison with Adriamycin (ADM), cisplatin (CDDP) and paclitaxel. The ability of MS-247 to associate with the DNA minor groove was assessed by measuring quenching of Hoechst 33342 fluorescence. DNA-DNA interstrand crosslinks (ICL) were detected by an alkaline elution assay for cellular DNA and a band-shift assay using the plasmid pBR322. The effects of MS-247 on macromolecule synthesis (DNA, RNA and proteins) were examined by measuring incorporation of the radiolabeled precursors. Results: MS-247 exhibited in vitro cytotoxicity with IC₅₀ values ranging 11 to 500 nM, and MS-247 given i.v. showed strong in vivo antitumor activity against i.p.-implanted L1210 leukemia cells and s.c.-implanted Colon26 carcinoma cells, and moderate activity against i.p.-implanted P388 leukemia cells but no apparent activity against s.c.-implanted B16 melanoma cells. MS-247 reversibly displaced Hoechst 33342 bound to DNA within a few minutes, and irreversibly formed ICL within 1–6 h in both the cell-free system and the cellular system. These results suggest that an association of MS-247 with the DNA minor groove occurred more quickly than ICL formation. The inhibition of DNA synthesis was more prominent than the inhibition of RNA and protein synthesis in L1210 cells exposed to MS-247, and a 6-h incubation with MS-247, which formed apparent ICL in the cellular system, strongly inhibited DNA synthesis. This result suggests that impairment of DNA replication preceded the inhibition of RNA and protein synthesis and that ICL formation greatly contributed to the inhibition of macromolecule synthesis. Conclusion: The results of this study suggest that MS-247 exerts its cytotoxic effect through impairment of DNA function by getting into the minor groove of DNA and subsequently forming ICL. MS-247 has potent antitumor activity with a different spectrum from the activity of clinically proven antitumor agents such as paclitaxel, ADM and CDDP against several murine tumor cell lines. This result suggests that MS-247 may be useful for the treatment of human cancers. Received: 6 July 1999 / Accepted: 14 February 2000     

THE ANTITUMOR ACTIVITIES OF GNIDIMACRIN ISOLATED FROM STELLERA CHAMAEJASMEL．

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In vitro induction of apoptosis and in vivo effects of a flavone nitroderivative in murine mammary adenocarcinoma cells

We explored the in vitro and in vivo mechanism of antitumor action of the synthetic flavonoid 2′‐nitroflavone on LM3 murine mammary adenocarcinoma cells. In vitro assays showed that 2′‐nitroflavone increased the population of LM3 hypodiploid cells and produced a typical ladder of DNA fragmentation. Apoptotic cell death was also characterized by the activation of caspase‐8, ‐9 and ‐3, by an increment in the expression levels of the proapoptotic protein Bax and by the release of cytochrome c to cytosol. The in vivo effect of 2′‐nitroflavone on tumor growth was studied in BALB/c mice injected subcutaneously with LM3 cells. Results showed that tumor volume and weight were significantly reduced at doses of 10 and 40 mg/kg of 2′‐nitroflavone, respectively. Apoptotic cells were identified by TUNEL assay in tumor slices from mice treated with 10 mg/kg of 2′‐nitroflavone. Western blot analysis of tumor lysate supernatants from treated mice revealed an upregulation of the total levels of Bax and Fas receptor. In addition, administration of 40 mg/kg of 2′‐nitroflavone to nontumor‐bearing mice showed no histopathological effects on different organ tissues. This is the first report of the in vivo growth inhibitory effect of 2′‐nitroflavone as an apoptotic agent likely useful for mammary adenocarcinoma treatment. © 2009 UICC     

Antitumor activity and hematotoxicity of a new, substituted dihydrobenzoxazine, FK973, in mice

FK973, a new, substituted dihydrobenzoxazine (11-acetyl-8-carbamoyloxymethyl-4-formyl-14-oxa-1,11- diazatetracyclo[7.4.1.0.0]tetra-deca-2,4,6-trien-6,9-diyl diacetate), was obtained by chemical modification of a novel antibiotic which was isolated from the fermentation products of Streptomyces sandaensis No. 6897. FK973 had cytotoxic effects against in vitro cultured human and murine tumor cells. FK973 in doses of 0.032-5.6 mg/kg (i.p.) had stronger antitumor activities and higher chemotherapeutic ratio than mitomycin C against such murine ascitic tumors as P388 and L1210 leukemia, B16 melanoma, M5076 reticulum cell sarcoma of ovarian origin, Colon 26 carcinoma, Ehrlich carcinoma, and MH134 hepatoma. In tests against murine and human solid tumors implanted s.c. in normal mice and nude mice, respectively, FK973 (i.v.) inhibited growth of murine tumors (M5076 sarcoma, Colon 38 carcinoma, B16 melanoma, and Lewis lung carcinoma) by 66-100% and human tumors (LX-1 lung, MX-1 mammary, and SC-6 stomach carcinoma) by 84-99%. In studies with drug-resistant P388 leukemia, FK973 was also effective against vincristine-resistant P388, moderately effective against mitomycin C (MMC)- and adriamycin-resistant P388, and partially effective against cyclophosphamide-resistant P388 cells in mice. Leukopenic effects of FK973 and MMC in mice were comparable at doses which gave antitumor activity almost equally. FK973 had no effect on the numbers of platelets and red blood cells, whereas MMC markedly decreased both. FK973 decreased the numbers of colony forming units in spleen and in culture and the effect was less than that of MMC. Therefore, FK973 may give weaker myelosuppression than MMC. The results suggest that FK973 will be a beneficial drug for the treatment of cancer.     

Antitumor effect of oxycellulose as a hemostatic during operation

Oxycellulose, a hemostatic agent used in operation showed antitumor effect in vitro on a murine hepatic cell carcinoma (MH 134), a murine fibrosarcoma (Meth A) and a murine colon carcinoma (Colon 26). The effect was also confirmed in vivo by the survival of mice inoculated with Meth A or MH 134. Eighty milligrams per mouse of this agent, however, showed a toxicity rather than an antitumor effect. The antitumor effect of oxycellulose on Meth A did not compare with that of etoposide or mitomycin C in vivo. The antitumor effect on MH 134 was equal to that of etoposide but not mitomycin C. Oxycellulose inhibited tritium thymidine uptake into Colon 26 cells to the same extent as 5-fluorouracil and mitomycin C and it caused 51Cr-labelled Colon 26 cells but not from 5-fluorouracil or mitomycin C. Oxycellulose decreased a larger number of viable tumor cells than 5-fluorouracil or mitomycin C when the tumor cells were incubated for 24 hours at 37 degrees C. DNA histogram with MH 134 cells showed oxycellulose decreased a ratio of tumor cells in S-phase. These results suggest that the antitumor effect of oxycellulose is cytocidal and phase-specific.     

FK317: a novel substituted dihydrobenzoxazine with potent antitumor activity which does not induce vascular leak syndrome

Purpose: FK973, a substituted dihydrobenzoxazine, is an antitumor antibiotic which has shown high therapeutic efficacy in a phase I study, but its development has been abandoned because of the side effect of vascular leak syndrome (VLS) in the clinical study. This study was performed to investigate whether or not FK317, a new benzmethoxy derivative of FK973, retains the antitumor activity of FK973 without the side effect of VLS. Methods: VLS was evaluated by the volume of pleural effusion in rats. Cytotoxic activities were determined by a tetrazolium-based colorimetric assay (MTT assay) against murine (B16, P388) and human (HeLa S3, KB) tumor cell lines. Antitumor activities against murine ascitic leukemia (P388, L1210), murine solid tumors (reticulum cell sarcoma M5076, Colon 38 carcinoma) and human xenografts (mammary carcinoma MX-1, lung carcinoma LX-1) were examined. Results: FK973 (1.8 mg/kg) given i.v. to rats induced pleural effusion, one of the elements of VLS, 36 days after the first dosing, but did not 28 days after dosing. This model reflects clinical VLS delayed-type effusion with high protein concentrations. In contrast, FK317 (1.0–3.2 mg/kg) did not induce pleural effusion at all. FK317 had stronger cytotoxic effects against in vitro cultured B16, P388, HeLa S3 and KB tumor cell lines, and in in vivo experiments, FK317 showed equivalent antitumor activity against P388, M5076 and MX-1, and more potent antitumor activity against L1210, Colon 38 and LX-1 compared with FK973. Conclusion: These results suggest that FK317 retains the antitumor activity of FK973 and does not induce VLS, and FK317 is a drug with high clinical potential for treating tumors in humans. Received: 22 May 1997 / Accepted: 12 November 1997     

The antibody‐based targeted delivery of interleukin‐4 and 12 to the tumor neovasculature eradicates tumors in three mouse models of cancer

Preclinical studies with recombinant murine interleukin 4 (IL4) in models of cancer have shown potent tumor growth inhibition. However, systemic administration of human IL4 to cancer patients exhibited modest antitumor activity and considerable toxicities. To improve the therapeutic index and reduce side effects of this cytokine, we developed of a novel “immunocytokine” based on sequential fusion of murine IL4 with the antibody fragment F8 (specific to the alternatively spliced extra‐domain A of fibronectin, a marker for tumor‐angiogenesis) in diabody format. The resulting fusion protein, termed F8‐IL4, retained full antigen‐binding activity and cytokine bioactivity and was able to selectively localize on solid tumors in vivo. When used as single agent, F8‐IL4 inhibited tumor growth in three different immunocompetent murine cancer models (F9 teratocarcinoma, CT26 colon carcinoma and A20 lymphoma). Furthermore, F8‐IL4 showed synergistic effects when coadministered with immunocytokines based on IL2 and IL12. Indeed, combination therapy with an IL12‐based immunocytokine yielded complete tumor eradication, in spite of the fact that IL4 and IL12 display opposite immunological mechanisms of action in terms of their polarization of T‐cell based responses. No weight loss or any signs of toxicity were observed in treated mice, both in monotherapy and in combination, indicating a good tolerability of the immunocytokine treatment. Interestingly, mice cured from CT26 tumors acquired a durable protective antitumor immunity. Depletion experiments indicated that the antitumor activity was mediated by CD8+ T cells and by NK cells.     

Antitumor effects of novel compound,guttiferone K,on colon cancer by p21Waf1/Cip1‐mediated G0/G1 cell cycle arrest and apoptosis

Low selectivity is one of the major problems of currently used anticancer drugs, therefore, there is a high demand for novel, selective antitumor agents. In this study, the anticancer effects and mechanisms of guttiferone K (GUTK), a novel polyprenylated acylphloroglucinol derivative isolated from Garcinia cowa Roxb., were examined for its development as a novel drug targeting colon cancer. GUTK concentration‐ and time‐dependently reduced the viability of human colon cancer HT‐29 cells (IC₅₀ value 5.39 ± 0.22 μM) without affecting the viability of normal human colon epithelial CCD 841 CoN cells and induced G₀/G₁ cell cycle arrest in HT‐29 cells by down‐regulating cyclins D1, D3 and cyclin‐dependent kinases 4 and 6, while selectively restoring p21Waf1/Cip1 and p27Kip1 to levels comparable to those observed in normal colon cells, without affecting their levels in normal cells. GUTK (10.0 μM) induced cleavage of PARP, caspases‐3, ‐8 and ‐9 and chromatin condensation to stimulate caspase‐3‐mediated apoptosis. The addition of a JNK inhibitor, SP600125, partially reversed GUTK‐induced caspase‐3 activity, indicating the possible involvement of JNK in GUTK‐induced apoptosis. Furthermore, GUTK (10 mg/kg, i.p.) significantly decreased the tumor volume in a syngeneic colon tumor model when used alone or in combination with 5‐fluorouracil without toxicity to the mice. Immunohistochemical staining of the tumor sections revealed a mechanism involving an increase in cleaved caspase‐3 and a decrease in cell proliferation marker Ki‐67. Our results support GUTK as a promising novel, potent and selective antitumor drug candidate for colon cancer.     

Low‐intensity ultrasound and microbubbles enhance the antitumor effect of cisplatin

Cell permeabilization using microbubbles (MB) and low‐intensity ultrasound (US) have the potential for delivering molecules into the cytoplasm. The collapsing MB and cavitation bubbles created by this collapse generate impulsive pressures that cause transient membrane permeability, allowing exogenous molecules to enter the cells. To evaluate this methodology in vitro and in vivo, we investigated the effects of low‐intensity 1‐MHz pulsed US and MB combined with cis‐diamminedichloroplatinum (II) (CDDP) on two cell lines (Colon 26 murine colon carcinoma and EMT6 murine mammary carcinoma) in vitro and in vivo on severe combined immunodeficient mice inoculated with HT29‐luc human colon carcinoma. To investigate in vitro the efficiency of molecular delivery by the US and MB method, calcein molecules with a molecular weight in the same range as that of CDDP were used as fluorescent markers. Fluorescence measurement revealed that approximately 10⁶–10⁷ calcein molecules per cell were internalized. US–MB‐mediated delivery of CDDP in Colon 26 and EMT6 cells increased cytotoxicity in a dose‐dependent manner and induced apoptosis (nuclear condensation and fragmentation, and increase in caspase‐3 activity). In vivo experiments with xenografts (HT29‐luc) revealed a very significant reduction in tumor volume in mice treated with CDDP + US + MB compared with those in the US + CDDP groups for two different concentrations of CDDP. This finding suggests that the US–MB method combined with chemotherapy has clinical potential in cancer therapy. (Cancer Sci 2008; 99: 2525–2531)     

Inhibition of N‐linked glycosylation by tunicamycin enhances sensitivity to cisplatin in human head‐and‐neck carcinoma cells

Tunicamycin (TM), a naturally occurring antibiotic, blocks the first step in the biosynthesis of N‐linked oligosaccharides in cells. In this study, we investigated whether changes in N‐linked glycosylation affect the sensitivity of head‐and‐neck carcinoma cell lines to cis‐diaminedichloroplatinum(II) (cisplatin) in vitro and in vivo. In vitro treatment of the IMC‐3 and KB cell lines with TM significantly decreased the 50% inhibitory concentration (IC₅₀) of cisplatin, as determined by the MTT assay (24.15 to 10.97 μg/ml, p < 0.05). In addition, TM significantly decreased the IC₅₀ of cisplatin against established cisplatin‐resistant IMC‐3/CR cells (>100 to 14.4 μg/ml, p < 0.05) to levels similar to those against parental IMC‐3 cells. TM treatment decreased the number of Con A‐ and L‐PHA‐binding sites on the surface of tumor cells but had no effect on the intracellular platinum concentration. Induction of apoptosis in vitro by TM plus cisplatin in combination was increased compared with that by cisplatin alone. Furthermore, in vivo administration of TM plus cisplatin in combination significantly inhibited local tumor growth in the cisplatin‐resistant in vivo C3H/He mouse model as compared with the control group (p < 0.05) and increased in vivo apoptosis of tumor cells. Our results suggest that the manipulation of glycosylation by TM in tumor cells might be a useful therapeutic strategy for successful chemotherapy using cisplatin against head‐and‐neck cancer. Int. J. Cancer80:279–284, 1999. © 1999 Wiley‐Liss, Inc.     

BMI1 silencing enhances docetaxel activity and impairs antioxidant response in prostate cancer

The BMI1 oncogene promotes prostate cancer (PC) progression. High B‐cell‐specific Moloney murine leukemia virus integration site 1 (BMI1) expression predicts poor prognosis in PC patients. Recent evidence suggests that BMI1 may also play a role in docetaxel chemoresistance. However, mechanisms and clinical significance of BMI1‐related chemoresistance have not been investigated. For this purpose, BMI1 was silenced in 2 PC cell lines (LNCaP and DU 145). Cell proliferation and apoptosis after docetaxel treatment were measured. Guanine oxidation was assessed by in‐cell western. Global gene expression analysis was performed on BMI1 silenced cells. Oncomine database was used to compare in vitro data with gene expression in PC samples. BMI1 silencing had no effect on cell proliferation but significantly enhanced docetaxel‐induced antitumor activity. Gene expression analysis demonstrated that BMI1 silencing downregulates a set of antioxidant genes. Docetaxel treatment increased guanine oxidation, whereas the antioxidant N‐acetyl cysteine rescued docetaxel‐induced cell death. Examination of clinical datasets revealed a positive correlation of BMI1 and antioxidant gene expression. BMI1‐controlled antioxidant genes were predictive of poor prognosis in PC patients. In conclusion, BMI1 enhances antioxidant response, thereby allowing PC survival after docetaxel‐based chemotherapy. BMI1‐controlled antioxidant genes are overexpressed in aggressive PC and should be tested as predictors of chemotherapy failure.     

Drug‐regulatable cancer cell death induced by BID under control of the tissue‐specific,lung cancer‐targeted TTS promoter system

Gene therapy and virotherapy are among the approaches currently being used to treat lung cancer. The success of cancer gene therapy depends on treatments where different types of tumors can be selectively targeted and destroyed without affecting normal cells and tissue. Previously, we described a promoter system (TTS) that we designed that is specifically targeted to lung cancer cells but which does not affect other types of cells including stem cells. In our study, we have enhanced the utility of the TTS system by inserting the pro‐apoptotic gene BH3 domain interacting death agonist (Bid) into the TTS promoter system (TTS/Bid) to create a drug regulatable lung cancer‐specific gene therapy. A recombinant adenoviral vector was used to introduce TTS/Bid (Ad‐TTS/Bid) into lung cancer cells. BID expression and apoptosis occurred in A549 pulmonary adenocarcinoma cells but little Bid expression or apoptosis occurred in MCF7 breast cancer cells or in normal human lung fibroblasts. The use of cisplatin enhanced the processing of full length BID to t‐BID which significantly increased lung cancer‐specific cell death. In in vivo experiments, intraperitonal injection of cisplatin enhanced the antitumor effects of the vector in a lung cancer xeno‐graft mouse model. Moreover, dexamethasone effectively suppressed exogenous BID expression and the antitumor effect of Ad‐TTS/Bid both in vitro and in vivo. Here, we describe the efficacy of the use of cisplatin and dexamethasone with the anti lung cancer promoter system (Ad‐TTS/Bid) for a safe and effective gene therapy against advanced lung cancer. © 2009 UICC     

Antitumor activity on murine tumors of a novel antitumor benzoylphenylurea derivative,HO-221

Summary A novel antitumor compound,N-[4-(5-bromo-2-pyrimidinyloxy)-3-chlorophenyl]-N-(2-nitrobenzoyl) urea (HO-221) was evaluated for its antitumor activity in experimental tumor models. HO-221 preparation was given orally to tumor-bearing animals. The compound exhibited significant effects against various tumors such as P388 and L1210 leukemias; M5076 reticulum-cell sarcoma; colon 38 carcinoma; human xenografts MX-1, LX-1, GA-1, and Co-1; Lewis lung carcinoma; sarcoma 180; and Walker 256 carcinosarcoma and was especially effective against solid tumors. However, its effect on murine B16 melanoma was moderate. Intermittent administration of HO-221 produced better results. The effects of HO-221 on human tumor xenografts were compared with those of other antitumor agents. HO-221 showed activity against LX-1 lung and Co-1 gastrointestinal tumor and was also effective against advanced-stage L1210 leukemia and Lewis lung carcinoma. Furthermore, the effect of HO-221 on drug-resistant tumors was examined using murine leukemias L1210 and P388. It showed no cross-resistance with the known antitumor agents Adriamycin (ADM), daunomycin (DM), vincristine (VCR), mitomycin C (MMC), cisplatin (CDDP), 5-fluorouracil (5-FU), cytosine arabinoside (Ara-C), methotrexate (MTX), cyclophosphamide (CPA), or carboquone (CQ), and collateral sensitivity to HO-221 was found in MMC-, CDDP-, and CPA-resistant sublines. HO-221 exhibits significant reproducible, broadspectrum antitumor activity against experimental tumors as well as human neoplasms.     

CXCR4 Inhibition with AMD3100 Sensitizes Prostate Cancer to Docetaxel Chemotherapy

Several in vitro and in vivo models have revealed the key role of CXCR4/CXCL12 axis in tumor-stroma interactions. Stromal cells present in the tumor microenvironment express high levels of CXCL12 protein, directly stimulating proliferation and migration of CXCR4-expressing cancer cells. This specific prosurvival influence of stromal cells on tumor cells is thought to protect them from cytotoxic chemotherapy and is postulated as a possible explanation for the minimal residual disease in hematological and solid cancers. Therefore, CXCR4/CXCL12 signaling is an attractive therapeutic target in cancer, as proven in preclinical leukemia mouse models, where CXCR4 inhibition sensitized cancer cells to conventional chemotherapy. This study investigates whether inhibition of CXCR4 with the specific inhibitor AMD3100 sensitizes human prostate cancer cells to docetaxel. We showed that both mouse and human stromal cell lines have a protective effect on PC3-luc cells by promoting their survival after chemotherapy. Furthermore, we demonstrated that AMD3100 sensitizes PC3-luc cells to docetaxel. In a subcutaneous xenograft mouse model of human prostate carcinoma, we showed that a combination of docetaxel and AMD3100 exerts increased antitumor effect compared with docetaxel alone. We concluded that CXCR4 inhibition chemosensitizes prostate cancer cells, both in vitro and in vivo. To explore the relevance of these findings, we analyzed CXCR4 expression levels in human prostate cancer samples. We found that cancer cells present in bone metastatic lesions express higher CXCR4 levels relative to the cells present in primary tumors and lymph node metastatic lesions. These findings underscore the potential of CXCR4 inhibitors as chemosensitizing agents.     

Lack of interleukin‐6 in the tumor microenvironment augments type‐1 immunity and increases the efficacy of cancer immunotherapy

Conquering immunosuppression in tumor microenvironments is crucial for effective cancer immunotherapy. It is well known that interleukin (IL)‐6, a pleiotropic cytokine, is produced in the tumor‐bearing state. In the present study, we investigated the precise effects of IL‐6 on antitumor immunity and the subsequent tumorigenesis in tumor‐bearing hosts. CT26 cells, a murine colon cancer cell line, were intradermally injected into wild‐type and IL‐6‐deficient mice. As a result, we found that tumor growth was decreased significantly in IL‐6‐deficient mice compared with wild‐type mice and the reduction was abrogated by depletion of CD8⁺ T cells. We further evaluated the immune status of tumor microenvironments and confirmed that mature dendritic cells, helper T cells and cytotoxic T cells were highly accumulated in tumor sites under the IL‐6‐deficient condition. In addition, higher numbers of interferon (IFN)‐γ‐producing T cells were present in the tumor tissues of IL‐6‐deficient mice compared with wild‐type mice. Surface expression levels of programmed death‐ligand 1 (PD‐L1) and MHC class I on CT26 cells were enhanced under the IL‐6‐deficient condition in vivo and by IFN‐γ stimulation in vitro. Finally, we confirmed that in vivo injection of an anti‐PD‐L1 antibody or a Toll‐like receptor 3 ligand, polyinosinic‐polycytidylic acid, effectively inhibited tumorigenesis under the IL‐6‐deficient condition. Based on these findings, we speculate that a lack of IL‐6 produced in tumor‐bearing host augments induction of antitumor effector T cells and inhibits tumorigenesis in vivo, suggesting that IL‐6 signaling may be a promising target for the development of effective cancer immunotherapies.     

Antitumor activity of gold(III)‐dithiocarbamato derivatives on prostate cancer cells and xenografts

Among the nonplatinum antitumor drugs, gold(III)‐dithiocarbamato derivatives have recently attracted considerable attention due to their strong in vitro and in vivo antiproliferative activity and reduced renal toxicity. Some of them, namely [AuCl₂(DMDT)] (compound 1 ) and [AuBr₂(ESDT)] (compound 2 ), have shown to be highly active against the androgen‐resistant prostate cancer cell lines PC3 and DU145, both inhibiting cell proliferation in a dose‐dependent way, and are more active than the reference drug cisplatin (cis‐[PtCl₂(NH₃)₂]). In particular, [AuCl₂(DMDT)] was proved cytotoxic against cisplatin‐resistant R‐PC3 cells, with activity levels comparable to those induced on the parent cisplatin‐sensitive PC3 cells, ruling out the occurrence of cross‐resistance phenomena. Moreover, it causes early cell damage, slightly affecting the cell cycle, thus suggesting a different mechanism of action from clinically established platinum‐based drugs. In fact, the investigated gold(III) complex alters mitochondrial functions, promoting mitochondrial membrane permeabilization and Cyt‐c release, stimulating ROS generation, and strongly inhibiting the activity of the selenoenzyme TrxR, which is overexpressed in prostate cancer and associated with the onset of drug resistance. In addition, it induces apoptosis, caspase activation, Bcl‐2 downregulation and Bax upregulation, reduces the expression of the phosphorylated form of the EGFR, and it inhibits PC3 cell migration. Finally, the treatment of PC3 prostate tumor‐bearing nude mice with [AuCl₂(DMDT)] significantly inhibited tumor growth in vivo, causing minimal systemic toxicity. Altogether, our results confirm that these gold(III)‐dithiocarbamato derivatives have potential for the treatment of prostate cancer.     

Antitumor activity of cis-dichlorodiammineplatinum(II) and its effect on cell cycle progression

Antitumor activity of cis-dichlorodiammineplatinum(II) (cisplatin) on various mouse transplantable tumors was investigated. Cisplatin was active against a wide variety of the following tumor systems: L1210 leukemia, P388 leukemia, B16 melanoma, colon tumor 38, Ehrlich ascites and solid carcinoma, WHT squamous cell carcinoma, and human stomach cancer G/S heterotransplanted in nude mice. From the comparison of growth inhibitory effect by cisplatin with various other antitumor agents in cultured Ehrlich ascites carcinoma cells, cisplatin was found to be mainly a concentration depending drug, but also time depending, so that it was identified as a type Ib class drug proposed by Shimoyama. Effect of cisplatin on the cell cycle progression of Ehrlich ascites carcinoma cells in mice was studied by flow cytometry of DNA. At an early stage after administration of cisplatin, cell cycle progression was delayed in S phase and blocked in G2 phase. With the elapse of time block in G1 phase or G1-S boundary was observed and the cell population, partially synchronized in G1 phase or G1-S boundary, progressed slowly through S phase to be blocked in G2 phase finally.